Bip Overexpression induces tau hyperphosphorylation in
HEK293/tau cell
1
1,*
Zan-Chao LIU , Jian-Zhi WANG , Qing TIAN
1,*
1 Department of Pathology and Pathophysiology, Key Laboratory of Neurological
Disease of National Education Ministry and Hubei Province, Tongji Medical College,
Huazhong University of Science and Technology, Wuhan 430030, China.
*Corresponding author
Email: Liuzanchao2007@yahoo.cn
Abstract: Objective Alzhermer's Disease (AD) is the most common neurodegenerative
disease with the progressive cognitive impairment as the major clinical symptom.
Hyperphosphorylated microtubule associated protein tau is the major component of
intracellular neurofibrillary (NFTs), which is positively correlated with the
decline of learning and memory in AD patients. The upstream effectors leading to
tau hyperphosphorylation are still not fully understood. Endoplasmic reticulum (ER)
is responsible for the posttranslational processing of newly synthesized proteins
and ensuring proper protein folding and assembly. Lots of damages (such as oxidative
stress) can induce ER stress, which has been shown activated in the AD brain.
Increased level of Bip, an ER stress marker, was also shown in the temporal cortex
and the hippocampus of AD patients compared with age-matched controls. The present
study is to explore whether Bip overexpression could induce tau phosphorylation.
Methods Plasmid of Bip with EGFP-N1 vector was constructed and transfected into
HEK293/tau cell. The phosphorylation levels of tau protein and the activities of
the key tau phosphorylation related protein kinase glycogen synthase kinase-3
(GSK-3β), and the key protein phosphatase protein phosphatase 2A (PP2A), were
detected. Results (1)Bip overexpression in HEK293/tau cell induced increased
phosphorylation levels of tau at Ser214, Ser262, Ser396, Ser404, Thr205 and Thr231
epitopes. (2)The increased phosphorylation levels of GSK-3 at Tyr216 and decreased
phosphorylation levels at Ser9 were observed (indicating GSK-3 activation). (3)The
phosphorylation of PP2A catalytic subunit at Tyr307 had no significant change.
(4)Additionally, we also found increased Bip enhanced the association of tau and
GSK3β by immunoprecipitation. Conclusion
All these data confirmed that
overexpression of Bip could induce hyperphosphotylation of tau in vitro by
activating GSK-3 and enhancing the association of tau and GSK3β.
Keywords: Bip; tau; GSK3β